hello and thanks for reading.

last night on the interstate I heard some interesting noises coming from the back of my 300D. it sounded like rhythmic whumping - not a heavy knock but not a light click. i was going 80 mph. the noise wasn't constant, yet i couldn't determine what was triggering it. i slowed down, got over onto an exit ramp, and the noise then turned into an arhythmic heavy knock - such that the first thing i looked for when i got out of the car was something dragging along the road.

while driving i thought it might have been wheel bearing related, but after the sound on the offramp i am stumped. i haven't had a chance to check it out too much yet and i'm writing here looking for some leads as to what to look into first.

by the way, i did get back into the car after finding nothing obviously wrong, and drove the remaining 2 miles at 60 mph to get to my exit, and the next 2 miles at 30 mph to get home, and never heard another odd sound.

ideas?
thanks, jeff

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting

seem a little too vague to tell much.

take two aspirin and go to bed early.

call me in a couple days if you dont get better.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Can you support it safely on jackstands and run it, in an attempt to duplicate the noise and determine the source?

A "rythmic thumping" is usually related to a tire in some fashion. A "rythmic knock" is not.

Check the exhaust system for looseness too. You cannot overestimate the number of strange sounds that can occur. At least to rule it in or out.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Maybe that last road-kill encounter was hanging on for dear life to the very end.

The only other thing, and possible long shot, might be a broken sway bar end-link.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Seen Crash yet? (speaking of dragging road kill)

There was a wagon in that movie too! Nice beige one.

I just went through this with my 300SD, turned out the rear drivers side shock was bad, it would only compress about half way, therefore causing a sporadic thumping noise. I really can't figure out what would cause a shock to do that, but all I know is new shocks and it cured the thumping.

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87 300D - Running on Veggie oil; 260,000 plus miles; Original #14 head

Most on this forum are far more versed than I, but my experience w/ a sound that could be described as a popping/knocking sound turned out to be rear "half-shafts" or "axle-shafts." The sound was not constant and seemed more pronounced at cruising speeds and when braking. Because of less-than-glowing reviews of rebuilt units on this forum, I purchased new units from MB, which were not cheap (close to $300 each side) but I needed them fast as a friend had a space open in his shop and offered to put them in at no charge, and I didn't want to fool w/ replacing them again in the near future... I've no complaints so far...

Hopefully, your issue will turn out to be something less expensive!

Good luck!
--Chris

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Christopher
'06 Mercedes E350 station wagon (silver/black)
'85 Mercedes 300D (black pearl/palomino)
'85 Mercedes 300SD (smoke silver/burgundy)
'79 Cadillac Sedan DeVille

'05 Toyota Camry (because always running is nice)

'85 Mercedes 300D sold back to orig. owner 8-1-06
'84 Volvo 264GL Diesel, owned 2000-2013

I agree, when my right side half shaft was going out, it would make a clunk-clunk sound when let off the throttle and took right turns (highway exits). It would not make sounds in a straight line.

thanks to all who replied. over the past week i drove the car without any problems - around town. occasionally i got'er up to 60 on the boulevard but no noises.

tonight i chanced a drive to my parents (30 miles). i figured i'd turn around if i heard anything. i did hear something just past the 1/2 way point. the vibration started in slowly, as i was slowing down from 70 because of some roadhogging semis in front of me. the noise seemed the worse around 60, and i could definitely feel it too. i got off at an exit again, checked around under the car with a flashlight, got back on the road and viola - no sound.

i'm betting it is either in the half-axles or maybe right at the driveshaft. i will be inspecting deeper this weekend and will post my results.

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting

Look closely at your driveline carrier bearing(s). They should have full rubber intact and not allow a metal-to-metal contact at any point. Otherwise the possible causes of a noise like this are varied and numerous ranging from suspension bushings at any location through driveline issues from the frontmost u-joint to the side axle bearings.

I'd definitely want to get to the bottom of the noise before some rotating mass breaks loose under your car and threatens a traumatic driver impalement. That is.....unless you enjoy that sort of thing.

Good Luck!

I would first check the cv joint boots to see if they are still intact. If one is leaking you might save the day by changing the boot and filling with the proper amount of lubricant. You would of course clean the joint out really well if there was any chance even a little dirt got in there. Hopefully just a leaking boot. On the otherhand if the joint is going bad it will let you know in uncertain terms probably pretty soon anyways.

torn boot found today, passenger side. tomorrow jack stands will make for better inspecting.

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1984 300D "Brown (and Blue) Betty" Over 200k but the odometer isn't counting